Most of the time the time stamps shown on messages in chat show the time to me in my local time. The fourth post in this large image is mine and that's what time it was here.

But the previous two messages use yst. What is that? "your standard time"?

enter image description here ...cropped montage of this

enter image description here ...using tooltip

  • 5
    Presumably "yesterday", but I'm not sure. We tend to use relative time for anything within the last two days.
    – Catija
    Commented Jan 16, 2019 at 3:47

3 Answers 3


It's a bit easier to see if you look at a chat that has a bit more activity than the one in your example but we use a three-letter abbreviation for chat messages up to a week old.

So, something posted today just has the time, while something the prior day says "yst" for yesterday. Further out, we switch to days of the week, so "Sun" and "Sat" for Sunday and Saturday.

Chat timestamps showing "Sun" and "yst"

After you get to a week ago, you get to the full date with a three-letter month indication.

Chat message dates that are marked "Wed" and then "Jan 8"

If it were some sort of time zone indication, it'd (probably) be in all caps. As you can see from the "Sun" casing, we do follow those casing rules.


It means "yesterday". You can see a hint in the text above the last message: "1 day later".

Chat timestamps need to be compact, so it's not spelled out.

  • I suppose it's the last two of the three letters being st that's throwing me off. (e.g. est, dst) There's probably room for something like ystrd but I don't think I'm going to make that my first feature request. Thanks!
    – uhoh
    Commented Jan 16, 2019 at 3:51

To expand on the other answers, it indicates "yesterday" that, rather confusingly, is the period of time between 24h and 48h ago, regardless of the time of the day. So, for example, "Jan 15, 17:00" will be "yesterday" if visualized on "Jan 17, 16:00".
Note that this is not affected by your timezone.

  • 2
    "yesterday... all my troubles seemed so far away, now you've written this answer and made me think; oh what the heck is yesterday?"
    – uhoh
    Commented Jan 17, 2019 at 18:33
  • This is really interesting! I'm just curious if this is an SE-only convention, or if it is semi-standard? Is this from personal knowledge, or experimentation, or is there an SE link somewhere out there that states this? I'm asking because this appears that it could be the best and correct answer. Thanks!
    – uhoh
    Commented Jan 17, 2019 at 18:36
  • 1
    @uhoh personal experience, I spend way too much time on here and I tend to notice these things :P
    – Federico
    Commented Jan 17, 2019 at 20:32

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